There is compelling evidence that central serotonin neurons are involved in regulation of the cardiovascular system. However, the brain circuitry which underlies this influence is poorly understood. The major focus of this project is to investigate the effects of discrete neurotoxic of brain serotonin pathways on baroreceptor reflexes in conscious rats. The selective serotonin neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), will be injected into: (a) NTS, (b) medial forebrain bundle, (c) spinal cord or (d) lateral ventricles. Vehicle-injected controls will be included for each group. Within two weeks following microinjections of 5,7-DHT or vehicle, rats will be prepared with chronic arterial and venous catheters to permit direct recordings of blood pressure and heart rate and administration of drugs into conscious, unrestrained rats. Baroreceptor function will be assessed by dose-response curves for sodium nitroprus-side (0.5-20 Mug/kg) in each rat. Our findings to date indicate that baroreceptor function is largely spared following localized or global brain serotonin lesions.